AMINO-ACID-SEQUENCE OF THE ALPHA-SUBUNIT AND COMPUTER MODELING OF THEALPHA-SUBUNIT AND BETA-SUBUNIT OF ECHICETIN FROM THE VENOM OF ECHIS-CARINATUS (SAW-SCALED VIPER)

Echicetin, a heterodimeric protein from the venom of Echis cerinatus, binds to platelet glycoprotein Ib (GPIb) and so inhibits platelet aggr egation or agglutination induced by various platelet agonists acting v ia GPIb. The amino acid sequence of the beta subunit of echicetin has been reported and found to belong to the recently identified snake ven om subclass of the C-type lectin protein family. Echicetin alpha and b eta subunits were purified. N-terminal sequence analysis provided dire ct evidence that the protein purified was echicetin. The paper present s the complete amino acid sequence of the alpha subunit and computer m odels of the alpha and beta subunits. The sequence of alpha echicetin is highly similar to the alpha c and beta chains of various heterodime ric and homodimeric C-type lectins. Neither of the fully reduced and a lkylated alpha or beta subunits of echicetin inhibited the platelet ag glutination induced by von Willebrand factor-ristocetin or alpha-throm bin. Earlier reports about the inhibitory activity of reduced and alky lated echicetin beta subunit might have been due to partial reduction of the protein.